Pushbutton supervised fire detection system



Nov. 28, 1961 E. J. FREUNDT 3,011,161

PUSHBUTTON SUPERVISED FIRE DETECTION SYSTEM Filed March 3, 1959 ARMATUREOF V/BRATOR I 7'0 CLEAN CONTACTS /4 AND /5 RELAY TA IVSFOAMEA 5 scoAmAky 22 -/z I I NoRMAuY m I l1 CLOSZ-D 2 [5 SWITCH ,9 TfMPl-RATUREamen/v5 3 DEV/C58 (NORMALLY CLOSED) l6 Sol/N0 TRANSFORMER Zf SECONDARYDEV/cf My a m INVENTOR.

United States Patent O 3,011,161 PUSHBUTTON SUPERVISED FIRE DETECTIONSYSTEM 'Edmund John Freundt, Indianapolis, Ind.,

I assignor to Gladys E. Freundt Filed Mar. 3, 1959, Ser. No. 796,888 2Claims. (Cl. 340-214) Few residences have been provided with firedetection systems, partly because householders are reluctant to acceptthe associated burden of supervision, testing, or inspection of such asystem.

Thesimple series fire detection circuit, once it is installed in theaverage home, generally receives no supervision from the householder.With this type of circuit, vital signal wires may become defective, orfuses may blow; and the householder may not know about it unless a testswitch, if installed, is periodically used. The unsupervised series firedetection circuit possesses only limited responsive power to act. 'Saidaction may occur only when the fire detection circuit loses energy at atime when the signal-producing circuit is fully operative.

There are numerous vital elements of a simple series fire detectioncircuit, other than those in the fire detection circuit itself, whereinfailure may occur without causing the signal producing circuit to becomeresponsive. These elements are: availability of voltage from the supplytransformer; goodness of the transformer windings; goodness of primaryfuses or thermal elements in the system; goodness of the two supplylines to the relay circuit; goodness of the two contacts of the relay;goodness of the relay armature pivots or bearings; goodness ofthecontacts of the audible device when self-contact controlled; goodness ofthe coil of the audible device; goodness of the supply lines from therelay to the typical,- remote sound device. Even the relay coil andassociated fire detection circuit are vulnerable to failure withoutdetection, if such failure occurs in conjunction with a failure of anyof the vital elements just described.

The foregoing summary indicates the flimsy reliability characteristicsof the unsupervised series fire detection circuit. Such an unsupervisedcircuit has no inherent attributes of reliability. There has long beenrecognition of this fact, which emphasizes the need for some form ofautomatic supervision over the goodness of the circuit mentioned; andparticularly so, when installed in the average residence.

However, conventional types of supervised, closed circuit fire detectionsystems generally require double circuits and elaborate equipment. Suchsystems are prohibitive in cost for the average householder; and arecompletely unsuited for residential use, where the necessary skilledmaintenance for such a system is difiicult to obtain.

This invention contributes to the limited technology in this specificfield by a novel circuitry, including an improved sound device. Saidcombination obtains complete supervison over a normally closed firedetection circuit of the residential type noted. This supervision isachieved through suitable interconnection of the unsupervised, closedcircuit fire detection system with an open circuit door-signal system,such as the doorbell or chime circuit which exists in almost allresidences.

The basic functioning of this system is such that the door-signal systemfunctions in the usual manner from pushbutton operation, and failure ofany vital element in the fire detection system, or the door-signalsystem, renders the door-signal system inoperative. This system providesthorough supervision over all of the numerous elements in the firedetection system. v

The system achieves this result at the very modest cost of merchandisingthe additional equipment to add to an existing door-signal system. Suchequipment generally 3,011,161 Patented Nov. 28,1961

ice

consists of a universal package containing the additional door-signaltransformer, an inexpensive sounddevice of an improved type, and theequivalent of a relay. The

package is suitable for connection to any standard doorbell or chimecircuit.

The frequency of such supervision is determined by the frequency ofoperation of the associated'door-signal sys''.

door-signal system, by virtue of its associated nuisance problem wheninoperative, is a matter of considerable importance to most housewives,and to householders in general. Thus, it is only in rare cases that any'malfunc-.

tion in this system remains undetected for any length of time. rected inorder to eliminate the attendant household nuisance. Said system is thusan ideal medium for super-' vising'the goodness of an associated firedetectionsystem. I

This system of supervision is designed for commercial distribution as apackaged fire detection system for installation in the averageresidence. signal transformer, pushbutton, 'door signal device, andassociated wiring are utilized without any major alteration. Theadditional circuitry consists of the' installation of the closed circuittype of fire detectors, which are also furnished with the package; andconnection of this circuit to the door-signal system and the additionalequipment already noted. x

During the history of door-signal circuit utilization'and development ofthe simple, unsupervised series circuit for fire detection purposes, nocomposition has been offered to interconnect both circuits forsupervisory purposes. There is no evidence of associating the inherentsupervisory attributes of the ordinary doorbell pushbutton' withsupervision of a fire detectionsystem.

The principal reasons for the total absence of a useful composition inthis field will now be summarized. The purpose of this summary is toitemize each obstacle to the effectuation of the object ofthisinvention, with attendant specification of the novel compositionrequired-to overcome each obstacle, so that the original manner in whichthis invention satisfies each specification may readi ly becomeapparent.

j operation of the pushbuttonl 'The limitations which heretofore haveprevented the development of any useful composition in this specificfield are now listed, being given suitable reference num: bers, so thatthe novel achievements of this invention may conveniently be ascertainedby suitable comparison of the following numbered sections with thosesections appearing later, which describe the detailed operation of saidinvention. These limitations are:

(1) Characteristics of the common door-signal pushbutt0n.--This deviceis the simplest switching device known, consisting of a single .fixedcontact, and a single movable contact. It has only one realizablefunction, which is to close a circuit. To utilize said device .toachieve the opening. of a relay circuit, as is required to effectuatethe functioning of this system, requires novel use of circuits to obtainthe desired degree of circuit control without using the only. knownalternative. Said alternative is the use of a ballast resistor in serieswith the relay coil, and the shunting of the relay coil by the Such amethod imposes additional burden on the associated supply transformer;and, because of extremely stringent transformer output limitations,thismethodis not practical. 7 Y

(2) The characteristics ofstandard door-signal dvices. -Typi'calresidential-type;- door-signal devices. may

Malfunctions, once detected, are promptly c0r-' The existing door-J beclassified as low-current, self-contact-controlled, vibrating;high-current, self-contact-controlled, vibrating; or high current,non-vibrating, chime. Most residential doorsignal devices are of theinexpensive, high-current, vibrating type, when associated with adoorbell system. Most chimes are of the high current type, and arecapable of the equivalent of single-stroke action, being incapable ofproducing a continuous signal. The self-contact controlled type of sounddevice will not operate properly when connected in series with anotherdevice of the same type. A low current device will not operate properlywhen connected in parallel with a high current device, since theirperformance is determined by the peculiar characteristics of thestandard door-signal transformer. Normally, door-signal transformers arede signed to supply only one sound device. Also, a low current,contactless type of vibrator, or a low current chime, will not operateproperly when connected in series with a high current chime. In general,the joint use of door-signal devices requires a careful appraisal of theassociated impedance characteristics of the devices involved, and of thetransformer regulation characteristics.

Since a supervisory system of the type presented by this inventionrequires utilization of an additional sound device that must functionjointly with some existing sound device having incompatible operatingcharacteristics, said additional sound device should have some novelcharacteristic to effectuate the required joint operation.

(3) Characteristics of the available relay.The relay available for a lowcost interconnection of this type is necessarily inexpensive, since thecost of a high grade, hermetically sealed relay would result in aprohibitive rice level for the package. The low cost relay requiresconsiderable contact maintenance because of its construction, butprimarily because of the lack of use of its contacts. It is a fellestablished fact that the inherent tendency toward contact failure inthe low cost relay has been a significant deterrent in the developmentof a reliable, low cost, closed circuit type of fire detection systemfor the average residence.

It is also a well established fact that the typical low cost doorbellhas an astonishingly reliable contact life, and seldom fails because ofthe accumulation of chemical and organic films that persistently causethe failure of relay contacts. The basic reason for the reliableperformance of the ordinary vibrating doorbell resides in the fact thatthe self-contact controlled vibrator has associated with its frequentuse an automatic contact cleaning function. Said function is eifectuatedby virtue of the vibratory forces acting on the contacts.

Since a supervisory system of the type presented by this inventionrequires utilization of a relay, said device should not only be capableof functioning as a switching device, but should provide some form ofautomatic contact cleaning associated with complete utilization of allfeatures promoting circuit reliability which reside in the inherentqualities of the normally open door-signal system.

(4) T he. peculiar characteristics of the standard doorsignaltransfrmer.-The standard door-signal transformer is designed for usewith the usual doorbell installation, or its equivalent, where secondaryfuse protection is not feasible. Such transformers are'designed' to givesafe Operation under such conditions, in that adequate protectionagainst secondary short circuit current is provided by the internalconstruction of the transformer. Such transformers are limited byregulatory bodies to a maximum secondary short circuit current of sixamperes. The practical effect of this ruling is to limit the volt-amperecapacity of any one transformer, in the voltage ranges commonly usedwith doorbells or chimes, to volt-amperes.

Also, because of this limitation, door-signal trans: formers necessarilyhave very high impedances. Voltage regulation is extremely poor. Forexample, a typical doorbell transformer, rated at 10 volts open circuit,5 volt-amperes, delivers 1.2 amperes to a low cost doorbell with atransformer terminal pressure of only 3 volts.

The wide variation between no-load voltage and fullload voltage of suchtransformers imposes prohibitive limitations on the use of a door-signaltransformer for operation of a control relay. Such a relay coil, unlessoperated from an independant transformer, must be operated inconjunction with additional load, which, if controlled by said relaycontacts, would reduce relay coil voltage from a nominal value of aboutof the opencircuit voltage of its transformer, to about 40% of suchvoltage when the relay contacts applied additional, full load to thetransformer. Under such condition, the relay coil circuit, when closedto cause disconnection of the load, would obviously 'be incapable offunctioning.

For the reasons just described, a supervisory type of system of the typepresented by this invention requires novel use of a relay coil circuitto insure reliable operation of the relay under all possible conditionsof load applied by the relay contacts to the system.

(5) Characteristics of door-signal transformers with respect to capacityand with respect to parallel operati0n.The total load applied to a.system of this type would be the existing sound device, which'wouldcontinue to be supplied with voltage from the existing transformer, arelay coil, and an additional sound device. The relay coil wouldrepresent a burden of 4 volt-amperes; the additional sound device wouldrepresent a burden of 10 volt-amperes.

Using conventional connection schemes, the total system load wouldrequire a total of three transformers; one for the relay coil, one forthe existing sound device, and one for the additional sound device. Theonly manner in which such transformers could be utilized is throughparallel operation of all transformers, or allocation of individual loadto individual transformers.

Parallel operation of such transformers would pose the immediateproblems of how to deenergize the relay coil without the use of aballast resistor; the necessary addition of secondary protective devicesto limit the secondary wiring short circuit current to the valuepermitted for one transformer; and the problem of how to operate deviceshaving widely divergent impedance characteristics from saidtransformers. In general, such problems have no practical answer;parallel operation of transformers being impossible under the conditionslimiting switching and impedance matching in this interconnection.

Individual operation of transformers would require means to disconnectthe individual transformers from their associated load. This wouldimpose an impossible condition on the only available switching device,which is a simple, double-contact pushbutton.

Study of the limitations just described indicates that the onlypractical manner in which successful operation of an interconnectedsystem of the type noted may be efiectuated is through the use of anovel circuit arrangement, using only two transformers, one being theexisting transformer; said circuit permitting the utilization of theadditional transformer for energizing the relay coil alone; or forenergizing the relay-contact switched load when the relay coil is notenergized; or for energizing both the relay coil and the additional loadduring the transient time interval required for the relay contacts toseparate in response to the application of voltage to the relay coil.Said circuit would thus be required to insure proper operating voltagefor the relay coil under all conditions of system operation, with noimposition of fixed losses in control resistors. In addition, suchcircuit control would be required that the door-signal circuit could notbe operative unless all vital functions of the fire detection circuitwere operative.

Before proceeding to the detailed description of the interconnectedsystems, an understanding of the improved sound device and relay notedunder (2) and (3) is neces sary.

In accordance with the specifications noted, this invention achieves animproved sound device which operates properly as a sound device with anyof the standard doorsignal devices commonly encountered in thisinterconnection. In addition, the improved sound device has thenecessary characteristics of a simple relay. The improved sound deviceachieves circuit simplicity and reliability heretofore not possible byreducing the four contacts previously associated with relay control of aself-contact-controlled vibrating sound device to one relay contact andone sound device contact.

Still another improvement resides in the derivation of the importantfunction of automatic contact cleaning.

The specifications for the improved sound device are simple. A sounddevice is used that has the necessary attributes to act as a contactlessvibrator, or as a selfcontact-controlled vibrator. The fixed contact ofsaid vibrator is replaced by the relay contact which is attached to themovable armature of a conventional relay.

The improved sound device has two possible contact arrangements. Thefirst location is at the free end of the armature. In this case, thedevice operates as a conventional, self-contact-controlled vibrator,Whose energy supply is also under the control of the associated,integral relay combination.

The second location for the contact arrangement is near the fixed end ofthe armature. In this case, the device is designated as a contactcleaning vibrator.

When used as a contact cleaning vibrator, the contacts, in theirdeenergized position, mate with normal contact pressure, and produce theminimum voltage drop associated with their inherent contact resistancecharacteristics. However, when the device is energized, the contactsreceive vigorous vibrations from the armature of the sound device. Thecontacts are subjected to rapid acceleration and deceleration throughthe small but finite amplitude of sound device armature travel. Thecontacts are hammered with numerous minute blows. A field of uniformsparking verifies the condition of minute contact separation, but saidseparation has no appreciable effect upon the proper operation of thesound device.

In the first contact arrangement, the contacts are subjected toadditional forces from the incidence of greater amplitude of armaturevibration, and the presence of contact arcing, with attendant heat andpitting of contacts. However, for both contact arrangements, the basicresult is a form of automatic contact cleaning. The rapid accelerationand deceleration of the contacts through their amplitude of travel, themechanical blows, and the faceto-face rubbing action are equivalent tohigh-grade maintenance activity in maintaining clean contacts, in thateach of the numerous operations of the improved sound device results inthe removal of loose films of chemical or of organic matter from thecontact faces. While such films, considered alone, are usually notdetrimental to contact conductivity, and are easily removed by anysimple v1- bratory process, said film, if not periodically removed,rapidly builds up to the point where contact failure is assured.Imaddition to the removal of the foreign matter noted, the incidence offrequent, vigorous vibrations from said device effectively discouragesinsect nesting, and its attendant toll of contact interference. Also,such vibration is a major force in preventing the accumulation of largerparticles of foreign matter; such particles generally being subjected todisintegrating forces before moisture and chemical actions solidify theminto armaturetravel blocking particles, or the like.

One of the preferred embodiments of this invention is now described.Reference is made to the accompanying drawing, which applies to adoorbell interconnection, but which also applies to a chimeinterconnection, with due consideration of the exception which isdescribed later.

The various circuit elements are listed as follows: 5, 6,

7, 8, 9, 13, 16, 18, 19, 2t), and 21 are connecting wires; 1, 2, 3, and4 are the terminals of transformer secondaries; 23 is the additionaltransformer, 24 is the existing transformer; pushbutton 22 is thecontrol device formerly controlling the original sound device 17 relaycoil 12 controls the mating of its contact 15 with contact 14; contact15 is mounted on the movable armature of the relay; contact 14 isattached to the fixed end of the armature of contact cleaning vibrator11, hereafter referred to as device 11; the functions of device 11 areto-produce an audible signal as a contactless vibrator, and to maintainvibration cleansing of contacts 14 and 15; normally closed temperaturesensitive element 10, wires 6, 9, and 21, plus relay coil 12, are theonly elements included in any reference to the fire detection circuit.

The system functions as follows: Transformers 23 and I 24 are connectedin cumulative series. Operation of pushbutton 22 shunts relay coil 12;device 11 is energized from transformer 23; contacts 14 and 15 areclosed, and vibrate through a very small amplitude in accordance withthe vibrations of device 11, said vibration of contacts having no effecton the vibration frequently ofdevice 11, yet insuring vibration cleaningof contacts 14 and 15; sound device -17 receives full voltage fromtransformer 24.

The supervisory function of this circuit is accomplished, since sounddevice 17 cannot operate unless every element in the entire system isoperative. The goodness of the entire system is indicated by appropriatesignals from device 11 and sound device 17; both signals being required,since device 11 must be audibly operative for the contact cleaningfunction to be operative; this function being considered of greatimportance for its maintenance activity.

The worst possible type of failure is completely supervised by thissystem. For example, the loss of secondary voltage from eithertransformer is supervised. The loss of secondary voltage fromtransformer 24 is noted by the loss of response from sound device .17.The loss of voltage from the secondary of transformer 23 transforms therelay into a vibrating buzzer; also device 11 is then inoperative.

During the condition of a fire, or equivalent interruption of the firedetection circuit, the relay coil loses energy, and relay contact 15mates with contact 14. Both sound device 17 and device 11 are now inseries with the total voltage of the two transformers. In spite of thefact that sound device 17 is almost always a selfcontact controlledvibrator, not adapted for series operation with any other similardevice, excellent performance is obtained from said device in its seriesoperation with device 11, since device 11, designed to operate as acontactless vibrator, will operate properly with any type of sounddevice. The excellent operation of sound device 17 during the emergencycondition noted is due to the unusual qualities of the circuit. Thecircuit is more fully described in the following paragraph.

In the doorbell system, the existing sound device is the major source ofsignal during a fire. The contact cleaning vibrator in the doorbellsystem is designed to operate under pushbutton control to maintain thecontact cleaning activity, and to give audible evidence of the presenceof-such activity. During the emergency condition, the contact cleaningvibrator functions as a current regulating impedance; and the productionof a fire detection signal, while evident, is of minor consequence.

Under emergency conditions, the disadvantages of unfavorable impedanceratios between the sound devices, fully controlled as they are. in thisinvention for relay voltage control purposes, become distinctadvantages. During this condition, practically all commonly used sounddevices Which may be connected to this system receive substantialovervoltage, resulting in the production of a vigorous signal which isWell suited for emergency' application.

The favorable distribution of voltages, during the em ergency conditionin the doorbell system is achieved through novel use of the ratiobetween the voltages of the two transformers; and the ratio between theimpedance of the contact cleaning vibrator and the impedance rangecommonly encountered with standard door-signal devices.

The impedance of the contact cleaning vibrator is established as afunction of the maximum and minimum impedances of the devices to bematched. The transformer ratio is fixed, since in the doorbell systemthe standard, existing transformer for the average installation is ratedat volts, 5 volt-amperes. The additional transformer is rated at 16volts, 1O volt-amperes. Novel use is made of this voltage distributionto enable the relay to receive adequate pull-in voltage during the Worstphases of operation of the system; which is when the relay circuit,having been opened for emergency purposes, or deenergized by loss ofvoltage to the entire system, or some fault in its wiring, is closed. Atsuch time, the transformers are fully loaded by the two sound devices,and such load cannot be removed until the relay coil receives sufiicientvoltage to operate its contact. The relay coil circuit is such that therelay coil receives voltage from the equivalent of a floating neutralcon nection, whose natural tendency is to maintain a voltage range whichassures reliable operation of the relay under a wide range of operatingconditions.

For the chime system, sound device 17 is replaced by device 11. Device11 in this system provides the emergency signal during a fire, since thechime is incapable of producing a continuous signal. The chime isconnected to replace device 11.

A summary of the improvements incorporated in this invention nowindicates complete agreement with the basic specifications noted under('1), (2), (3), (4), and (5). The major improvements advancing the artin this area are:

(or) Use of a simple, normally open, double contact pushbutton tocontrol energy supply to a relay coil Without the use of resistors, orthe addition of any fixed power loss, or the use of an additional relay.

(b) The use of a total of two door-signal transformers.

(c) Development of an improved sound device for use as a combined sounddevice, contact-cleaning vibrator, and current regulating impedance.

(d) Development of an improved sound device for use as a combinationsound device and relay, in which combination the minimum possible numberof operative and control contacts are required to effectuate theoperative function, and the relay control function.

(2) Development of a supervisory circuit wherein every vital function ofthe door-signal circuit and of the fire detection circuit must beoperative before the doorsignal device may operate.

(f) Development of a circuit utilizing unequal vol ages, the equivalentof a floating neutral, and a current regulating impedance, to provideproper operating voltage to a control relay, and to insure propercurrent flow to sound devices having incompatible impedancecharacteristics.

(g) Development of a circuit which discriminates between pushbuttoncontrol, and the inauguration of an emergency condition, in its abilityto provide over-voltage for the principal sound device utilized duringthe emergency condition.

There are various embodiments which may be devised for this invention.The numerous possible embodiments utilize the basic circuitry andequipment associated with the embodiments which are now described, orsuitable modifications thereof. The principal features of variousembodiments are noted as follows:

(a) In which the door-signal pushbutton shunts the secondary of adoor-signal transformer, to which the fire detection circuit relay isalso connected. Suitable circuits energize the sound devices fromadditional voltage sources.

([2) In which the system described by the accompanying drawing ismodified by disconnecting wire 13 from wires 2% and 21; wire 19 isremoved; and wire 13 is connected to terminal 3.

(c) In which the door-signal pushbutton shunts the contacts of the firedetection circuit relay, or shunts the suitably arranged contacts ofassociated, vibrating-type sound devices, or desired combinations ofsuch relay and sound device contacts.

(d) In which two identical transformers are connected in differentialseries with two sound devices, one being the contact cleaning vibrator.The midpoint of the transformer connection is in series with the contactsystem of the contact cleaning vibrator; said contacts are also inseries with the coil of the contact cleaning vibrator. The tiredetection circuit is connected to another transformer, where the relaycoil may be shunted by operation of the door-signal pushbutton.

What is claimed is:

1. A fire detection system consisting essentially of two interrelatedelectrical circuits, a fire-alarm circuit and an imperfection-detectioncircuit, said imperfectiondetection circuit being a doorbell systemsubjected to usage with reasonable frequency; a transformer having atapped secondary providing a relatively low voltage alternating currentfor operation of the doorbell system, a voltage for the temperatureresponsive portion of the fire alarm system, and a summation voltage foractuating the bell as a fire alarm; a plurality of temperature sensitivedevices which are normally closed but which open when subjected toexcessive temperature; a pair of contact points adapted to be held opennormally, to be closed whenever a temperature sensitive device issulficiently overheated to electrically open the temperature sensitivedevice, and to be vibrated during the closing of the doorbell button; anelectromagne-t in the temperature responsive portion of the fire alarmsystem said electromagnet normally being energized to urge the pair ofcontact points open; an electromagnet energized when the doorbell buttonis closed, said energized electromagnet vibrating the contact points.

2. A fire detection system comprising: a temperatureresponsiveelectrical circuit comprising a source of voltage, a plurality oftemperature sensitive devices which are normally closed but-which openwhen subjected to a preselected elevated temperature, and a pair ofcontact points; a system for detecting imperfections in said electricalcircuit opened by excessive temperature, said imperfection-detectionsystem comprising an electrical circuit comprising a source of voltage,an electromagnetic bell, and a manually operated doorbell button, and anelectromagnet positioned to vibrate said contact points of thetemperature responsive circuit, the electromagnetic bell failing to ringduring the depression of the doorbell button if there is anyimperfection in the temperature responsive circuit, and the voltagesources of the temperature responsive circuit and the voltage source ofthe door bell circuit being connected in series to direct a higher thannormal voltage to the electromagnetic bell in the event that thetemperature responsive circuit detects such preselected elevatedtemperature.

References Cited in the file of this patent UNITED STATES PATENTS

